Overall goal of the research: To understand how epidermal growth factor receptor tyrosine kinase activity leads to stimulation of arginase and the resultant vascular remodeling that is the hallmark of pulmonary hypertension. Pulmonary Hypertension is a life-threatening disease for which there is no cure. Epidermal growth factor receptors (EGFR) are critical for promoting growth, survival, and differentiation of cells. Arginase converts arginine to ornithine and urea and plays a critical regulatory role in NO synthesis by modulating the availability of L-arginine for NOS. During inflammatory stimuli, arginase is upregulated by EGFR activation and this pathway has no effect on NOS. We speculate that EGFR activation and enhanced arginase activity will increase proliferation and is thereby central to vascular remodeling in pulmonary hypertensive diseases. We will utilize exposure to low oxygen (hypoxia) as an in-vitro and in-vivo model of pulmonary hypertension. The studies described in the present proposal will address the role of EGFR activation in the pathogenesis of pulmonary hypertension. Specific aim 1: To test the hypothesis that hypoxia induced EGFR activation leads to arginase expression and a pro-proliferative state in human pulmonary microvascular endothelial cells. Pharmacological and siRNA inhibition of EGFR in hypoxia and normoxia will lead to decreased protein expression of Arginase and thereby promote tissue repair. Primary human pulmonary microvascular endothelial cells will be placed in hypoxia (1% oxygen) or normoxia (21% oxygen) while stimulated with No treatment, EGF, EGF+AG1478, EGFR siRNA, Arginase I and Arginase II siRNA. Specific aim 2: To test the hypothesis that EGFR inhibition prevents pulmonary vascular remodeling in a mouse model of pulmonary hypertension. Adult mice will be placed under hypoxic or normoxic conditions and the EGFR inhibitor AG1478 will be administered. Relevance: Results from these studies will provide mechanistic information regarding the role of EGFR in vascular proliferation and the pathogenesis of pulmonary hypertension. These studies will identify potential curative therapeutic targets for patients with pulmonary hypertension. [unreadable] [unreadable] [unreadable]